Law enforcement fanned out across Southern California on Thursday in a massive manhunt for a former Los Angeles police officer with a homicidal vendetta, who is suspected of killing a couple and fatally shooting another police officer in an ambush.

Christopher Jordan Dorner, 33, of La Palma, is said to be targeting police officers in a bid to avenge his firing from the Los Angeles Police Department in 2008 and, according to his manifesto, to clear his name.

Dorner's rampage led him from Irvine to San Diego to Riverside, as he engaged officers in gunfights at least twice.

By late Thursday the manhunt was focusing on the San Bernardino mountains where his vehicle, a Nissan Titan pickup, was found on fire in the parking lot of the Bear Mountain Ski Resort.

Christopher Dorner

Days before the officers were shot, Dorner had taunted his former law enforcement colleagues, writing in a 11,000-word manifesto that their efforts to find him or prevent more violence would be useless because he knew all their techniques. His words prompted police to dispatch at least 40 protective details to individuals named in the document.

"It is extremely worrisome and scary, especially to the police officers involved," LAPD Chief Charlie Beck said. "The Riverside officers were cowardly ambushed. They had no opportunity to fight back. No pre-warning. Imagine going about your workday having to worry about that threat."

Dorner has multiple weapons, including assault rifles, Beck said. He is described as a 6-foot-tall, 270-pound African-American man and a highly trained Navy veteran with awards for marksmanship.

Late Thursday, 125 law enforcement officers from various agencies searched the area around Big Bear Lake for Dorner, San Bernardino County Sheriff John McMahon said.

Hundreds more officers looked for Dorner across California and in Las Vegas, where he owns a home, or worked to protect the officers named as possible victims in Dorner's manifesto.

But every hour that passed meant an even wider area where he might be.

"Certainly he could be anywhere at this point, and that's why we're searching door to door," McMahon said during a Thursday press conference near where the truck was found.

The list of crimes attributed to Dorner grew Thursday. A Riverside police officer was shot dead in an ambush, and his trainee officer was shot and seriously injured. Two LAPD officers, who were in the area to protect some of those named in Dorner's manifesto, were injured when he opened fire on their car.

Dorner was fired from the LAPD under then-Chief William Bratton, who was also targeted in the manifesto.

"In my case, I was the chief of police that signed off on his discharge from the LAPD," Bratton said in an interview with CNN's Anderson Cooper, who was also named in the manifesto and received a package in the mail from Dorner.

"In terms of his grievances, I could understand his grievance directly toward me in my capacity as chief of police. A lot of police officers get discharged. None of them resort to the actions that this young man has taken."

An internal board found that Dorner lied when he accused a fellow officer of kicking a suspect arrested in July 2007 at a San Pedro hotel. His employment with the LAPD ended in 2008, according to Beck. Records indicate the firing was finalized in 2009.

Police said Dorner's rampage began Sunday night when Monica Quan, 28, and her fiance, Keith Lawrence, 27, were found shot to death in a car at their Irvine apartment complex garage.

Quan, an assistant women's basketball coach at California State University, Fullerton, was the daughter of former Los Angeles police captain Randal Quan, who represented Dorner in disciplinary hearings that resulted in his dismissal.

On Monday, Dorner posted his long, rambling manifesto that detailed his grievances against the LAPD, threatened police officers and their families, and demanded that his name be publicly cleared.

"The attacks will stop when the department states the truth about my innocence, PUBLICLY!!!" says the document, titled "Last resort."

Wednesday evening, Irvine police and the LAPD publicly announced Dorner was a suspect in the deaths of Quan and Lawrence.

Around 8:30 that night, police said, Dorner tried to steal a boat in San Diego, saying he wanted to go to Mexico. The boat apparently didn't function properly.

At 1:15 a.m. Thursday, Dorner was spotted more than 100 miles north of San Diego in Corona, near the home of one of the targets named in his manifesto. A police protection detail was already stationed near the house when a resident flagged down officers to report seeing Dorner's Nissan Titan.

Officers spotted the truck and chased it. At the Magnolia Avenue off-ramp from the northbound 15 Freeway, the driver opened fire on them. One officer suffered a graze wound to his head, "literally inches from killing him," Beck said.

Officers returned fire and Dorner fled, but they couldn't chase him because their car was damaged by gunfire, Beck said.

Twenty minutes later, 11 miles away in Riverside, police said Dorner fired a rifle at two Riverside police officers who were stopped at a red light.

A 34-year-old training officer, an 11-year veteran, was killed. A 27-year-old officer, who has been on the job less than a year, was shot. He was in stable condition Thursday. Diaz withheld the officers' names to protect their families.

Within hours, the manhunt spread throughout Southern California. Schools named by Dorner in his manifesto were put on lockdown or closed altogether. Law enforcement agencies from Pasadena to Fontana kept officers off motorcycles or barred single-officer patrols.

Two innocent bystanders were caught up Thursday in the search for Dorner. At 5:15 a.m., LAPD officers had a report of a pickup truck matching the description of Dorner's driving with its lights off in Torrance, near one of the primary protection targets.

Officers spotted the truck and fired on the vehicle hitting the people inside, who turned out to be female newspaper carriers.

Both were transported to hospital. One has a minor gunshot wound and is being released. The second had two gunshot wounds and is in stable condition.

"Tragically, we believe this was a case of mistaken identity by the officers," Beck said.

Asked what he would tell Dorner, the chief said, "I would tell him to turn himself in. This has gone far enough. Nobody else needs to die."

The public unease only increased through the day amid reports of Dorner or his property being spotted in San Diego and San Bernardino County.

About 2:30 a.m. Thursday, a passer-by found a wallet with a police badge and a picture ID of Dorner on a street near San Diego International Airport.

A report that Dorner was spotted later Thursday in San Diego also triggered a huge police response, though it apparently proved false. Police there said Dorner checked into a hotel in San Diego earlier this week.

Anderson Cooper, who Dorner urged in his manifesto to "keep up the great work," said on Twitter that Dorner had mailed a package to him that contained a note, DVD and a "coin shot thru with bullet holes."

After Dorner's truck was found at the Big Bear ski resort, officials began evacuating and locking down nearby schools, businesses and resorts, while law enforcement officers searched for Dorner on foot and with helicopters.

As the day closed, more than 100 mourners gathered at Riverside City Hall for a prayer vigil on behalf of the police officer killed that morning. Uniformed officers wore black bands over their badges for their colleague.

Gov. Jerry Brown announced the flags at the state Capitol would be flown at half-staff in honor of the fallen officer.

People with other tips can call LAPD Robbery Homicide detectives at 213-486-6860 or the 24-hour tip line at 877-LAPD-247 (527-3247).

Those who want to remain anonymous can call Crime Stoppers at 800-222-TIPS (8477) or text the organization by sending "LAPD" followed by a message to CRIMES (274637).